This invention relates to a control system for an engine and transmission. It is particularly described in relation to the marine environment wherein the engine is provided with a transmission for forward and reverse operation, the transmission including a clutch having a slipping capability through modulation of the pressure medium used for engagement of the clutch.
Powering of marine craft by internal combustion engines is well-known. Such arrangements usually include a transmission to provide a reverse capability to the output or propeller shaft. In such an arrangement, a balance between engine efficiency and propeller efficiency is necessary. It is well-known that internal combustion engines operate best at a particular speed. It is also well-known that propellers operate best at a particular speed of rotation unless the propeller is of the controllable pitch variety. In either case, a propeller is efficient in only one direction of rotation. Use of a controllable pitch propeller may facilitate reversal of the direction of propulsion of the craft in that change of direction of rotation of the propeller shaft is unnecessary. Therefore, a controllable pitch propeller equipped boat or marine craft usually does not require a transmission per se. A disadvantage of the controllable pitch propeller is the added initial expense of the pitch control mechanism and necessary complexity of the propeller shaft. Since propellers are one of the more vulnerable items in marine craft, damage to a controllable pitch propeller requiring repair or replacement entails a good deal more expense than the damaging of a fixed pitch propeller which quite frequently can be simply repaired by reshaping and balancing.
Ordinary fixed pitch propeller arrangements utilized in marine craft usually involve a forward and reverse transmission and some sort of clutching arrangement to engage the engine with the transmission. During operation the direction is selected and the clutch engaged before application of power to the engine. In order to change direction of the propeller shaft and thus acheive a change in direction of the propulsion of the marine craft itself the propeller shaft is disengaged from the engine through the use of the clutch, the reverse gear engaged and the propeller shaft reengaged with the engine. Operation through the water at slow speeds may cause the engine to "lug down" with a possible stalling during repeated reversals unless engine speed can be maintained above a certain minimum.
In work boats, such as fishing boats and crew boats, maneuverability is an important capability. Since efficient operation of the boat revolves around maneuvering, a capability to quickly back the boat without the possibility of an engine stall has resulted in boat operators "slipping" the clutch during maneuvering in order to maintain engine speed sufficiently above idle to prevent a stall. This concept also allows slow propeller speed at any engine speed for auxiliary loads and extra slow vessel speed. In order to accomplish this clutch slippage, the operator has been forced to utilize both the engine speed and direction control lever and the clutch control lever simultaneously. This, can hamper directional control of the boat since the operator must divert his attention from the helm to the engine controls.